Electrooptical apparatus



Jan. 12, 1932. H. E. was

ELECTROOPTICAL APPARATUS Filed Dec.

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ATTORNEY Patented Jan. 12, 1 932 UNITED STATESPATENT OFFICE HERBERT E. IVES, OE MONTCLAIR, NEW' JERSEY, ASSIGNOR T WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ELECTRODPTICAL APPARATUS This invention relates to electro-optical apparatus, and more particularly to photoelectric tubes.

The invention provides a stable and highly sensitive photo-electrictube characterized by having the photo-electric material in the form of a thin transparent la er.

Such a tube is prefera ly made by depositin: upon an electrically conductive cathode 0 within a highly "evacuated cell envelope a uniform thin transparent layer of photo electric material, any subsequent appreciable change of sensitivity of the cathode layer due to redistribution ofthe material within the envelope at ordinary room temperatures being prevented. In a preferred form of the invention the amount of photo-electric material which is present in the tube when it is finally completed is limited to that which is required to form a uniform film upon all the exposed interior surfaces of the tube, including the cathode, of such thickness that substantially maximum sensitivity obtains. The uniform layer on the exposed surfaces, other 3 than the cathode, prevents any appreciable changes in the sensitivity of the cathode layer due to redistribution of the material within the envelope on account of spontaneous deposition at ordinary room temperatures. The fihn may be further stabilized by providing the envelope with an atmosphere of inert'gas when the photo-electric material is more volatile than potassium.

A tube in accordance with the invention i may comprise. for example, a film of caesium on a highly polished platinum plate immersed in an atmosphere of argon gas at low pressure. Tubes of this kind have been found to be both sensitive and stable. In one method I of producing such a tube caesium vapor is allowed to diffuse very slowly into the evacuated envelope from a side tube. When maximum sensitiveness has been attained, the side tube is sealed ofi' and anatmosphere of inert gas such as argon is introduced to stabilize the film. x

The invention will now be described more in detail having referenceto the accompanying drawing which illustrates one example of practice.

The completed photo-electric tube comprises an envelope or enclosing vessel 5 having mounted therein a cylindrically shaped cathode 6 and a cylindrically shaped anode 7 of smaller'diameter located co-axially with the cathode 6. The cathode 6 is electrically connected to terminal 8, and the anode 7 to the terminal 9 through sealed-in wires.

The cathode 6 is preferably a highly polished platinum plate upon which there is deposited such athin film of light sensitive material that-maximum photo-electric sensi-' tivity obtains. The thin film is transparent. In a preferred form of tube the film consiSts of caesium and the electrodes are immersed in an atmosphere of argon, the envelope being sealed off at the points 10 and 11.

In the manufacture of a caesium argon filled tube. for example. enclosing vessel 5 is provided with a tribulation 12 for the introduc- 7 tion of the caesium and a tubulation 13 for purposes of evacuation and control of the pressure of the argon atmosphere. Tubulation 12 consists of aside tube 14 connected to another side tube 15 havinrr a reduced portion 16 in the connecting tube. Within the t side tube 15 is a metallic anvil 17 and an iron weight 18 which are adapted for breaking the evacuated capsule 19. The capsule 19 contains a supply of czesium which has previous;

ly been purified by distillation in vacuo. The

tubulation 13 comprises a side tube 20 for con nection to a vacuum pump and a chamber 21 containing charcoal which may be cooled by liquid air in well-known, manner. In the manufacture of a tube the equipment 1 as illustrated is connected to a vacuum pump and a high degree of vacuum maintained with suitable heating ofthe apparatus and electronic bombardment of the electrodes to' 0 substantially eliminate occluded gases. With the pump still operating the charcoal in side tube 21 is cooled with liquid air. Argonfgas is admitted through the tube 20. in wellknown manner, a quantity of which is absorbed by the charcoal in the tube 21. When i no' more argon will be absorbed and a high degree of vacuum is again obtained, the pump is sealed off at the restricted portion of tube 20.

- illuminated by connecting the electrodes 8 The caesium capsule 19 is now broken by raising the iron weight 18 with a magnet and allowing it to drop. Heat is then applied to the side tube to distill the caesium into the side tube 14 after which the side tube 15 is sealed off at the point 16. The caesium in the side tube 14 is now allowed to difiuse at ordinary room temperature into the vessel 5. Since the diffusion takes place very slowly, the caesium spreads itself uniformly over the metal parts of the tube and the increase in sensitiveness is watched while the tube is and 9 to a galvanometer in well-known manner. When the maximum sensitivity has been reached the side tube 14 is sealed ofi at the point 10. In order to stabilize this film an atmosphere of argon gas is now admitted to the vessel 5 by allowing the cooled charcoal in the tube 2l to warm up. When the pressure of argon within the vessel 5 reachesa desired value which may be between .05 mm. and .1 mm. of mercury, the tubulation 13 is sealed at the point 11 and the cell is ready for use.

The'atmosphere of inert gas serves also to provide gas amplification. The gas pressure is adjusted for maximum photo-electric amplification, this gas pressure being depend- A cut upon the electrode distance.

Light sensitive materials which meet the requirements of this invention are caesium,

rubidium, potassium, and sodium. Cacsium and rubidium are more volatile at ordinary room temperatures than potassium and sodium.

These materials may be used in the form of I thin films according to this invention withsuch as argon.

out immersion in an atmosphere of inert gas. In the case of caesium and rubidium, however, which metals are more 5 also be used as the cathode.

mod1fications, coming within the scope of the.

such pressure as to of film sensitivity.

volatile than potassium at ordinary room temperatures, it has been found preferable to employ such an atmosphere.

This invention is not limited to photo-elem t'ric tubes having any particular shape of electrodes or containing vessel. A glass vessel and a highly polished platinum cathode have been found tobe satisfactory. A magnesium coating on the inside of the glass vessel may appended claims, may be used.

What is claimed is 1. The method of making a photo-electric tube which comprises forming within an en-' velope electrically conductive cathode and anode, highly evacuating the envelope, and while in the evacuated condition depositing 5 on said cathode a uniform, thin, transparent film of photo-electric material more volatile than potassium, and subsequently providing the tube with an atmosphere of-inertgas at prevent a material change Other obvious 2. The method of making a photo-electric tube which comprises forming within an envelope electrically conductive cathode and anode, highly evacuating the envelope, de-' positing upon said. cathode while the envelope is in the evacuated condition a uniform, thin, transparent layer of caesium thinner than that which would be deposited by spontaneous deposition at average room temperature if an excessof caesium were present within the envelope, and modifying the atmosphere within the. tube to prevent an apreciable change of sensitivity of the cathode layer due to redistribution of the caesium within; the tube at ordinary room temperatures.

3. The method of making a photo-electric tube which comprises forming within an envelope electrically conductive cathode and anode, highly evacuating the envelope, de

positing on said cathode while the envelope is in the evacuated condition a uniform, thin,

transparent film of caesium by diffusion at ordinary room temperatures from a side tube I mert gas at such pressure as to prevent material change of film sensitivity. k 4. A photo-electric tube comprising an electrically conductive cathode and anode, a uniform, thin, transparent filmof photoelectric material on said cathode, and means for preventing a material change of sensitivity of the cathode film at ordinary room temperatures."

5. A photo-electric tube comprising an electrically conductive cathode and anode, a uniform, thin, transparent film of caesium on said cathode, and means for preventing a material change of sensitivity of the cathode film at ordinary room temperatures.

.6. A photo-electric tube comprising an electrically conductive cathode and anode, a uniform, thin, transparent film of caesium on said cathode, and an atmosphere of inert gas at such pressure as to prevent a material change of film sensitivity.

7 A photo-electric tube comprising an enclosing vessel. a pair of electrodes within thin film of said material is present on one of said electrodes of such thickness that substantially maximum sensitivity to light obtains, said photo-electric material being one capable of causing an increase of film thickness by spontaneous deposition at normal room temperatures,if a greater amount of the material were present.

8. A photo-electric tube' comprising an enclosing vessel, a pair of electrodes within said vessel, photo-electric material of such an amount within said vessel that a thin film ofsaid material is present on one of said elecrodes of such thickness that substantially maximum sensitivity to light obtains, said )hoto-electric material being more volatile .t normal room temperature than potassium, ,nd an: atmosphere of inert gas at low presme within said vessel. I

9. A photo-electric tube comprising an nclosing vessel, apair of electrodes within aid vessel, a thin layer ,of caesium spontaneaisly deposited on one of said electrodes to uch a thickness that substantially maximum ensitivity to light is obtained,'and an atmose )here of argon at low pressure within said 'esse 10. The method of making a photoelectric ube which comprises forming within an en- 'elope electrically conductive cathode and node, highly evacuating the envelope, prolucing upon said cathode .a uniform, thin, ransparent layer of photoelectric material hinner than that which would be produced y spontaneous deposition at average room emperature'if an excess of photo-electric material were present within the envelope, .nd modifying the atmosphere within the lube to prevent an appreciable change of ensitivity of the cathode layer due to redisribution of the material ,within the tube a rdinary room temperatures.

11. ,A photoelectric tube comprising an vacu'ated envelope housing an electrically :onduetive cathode and anode, said tube havng a uniform, thin,tra'nsparent film of phooelectric material deposited upon" all of its nterior exposed surfaces.

In witness whereof, I hereunto subscribe my name this 18th day of December, 1928.

v IERBEBT E. IVES. 

